Polyaxial bone anchor with helical capture connection, insert and dual locking assembly

ABSTRACT

A medical implant assembly includes a polyaxial bone anchor having a shank, a receiver, a lower compression insert with surfaces for closely receiving an elongate connecting member and a dual closure structure that may include a single flange or helical flange. The dual closure structure independently engages the connecting member and the lower compression insert. A threaded capture connection of the bone anchor includes a shank upper surface exclusively engaging the lower compression insert and a retainer threadably attached to the shank and spaced from the upper surface, the retainer configured for polyaxial motion with respect to the receiver prior to locking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/000,964 filed Oct. 30, 2007, incorporated by reference herein. Thisapplication is also a continuation-in-part of U.S. patent applicationSer. No. 11/522,503 filed Sep. 14, 2006 that is a continuation-in-partof U.S. patent application Ser. No. 11/024,543 filed Dec. 20, 2004, bothof which are incorporated by reference herein. This application is alsoa continuation-in-part of U.S. patent application Ser. No. 11/140,343filed May 27, 2005, incorporated by reference herein. This applicationis also a continuation-in-part of U.S. patent application Ser. No.10/986,377 filed Nov. 10, 2004, incorporated by reference herein. Thisapplication is also a continuation-in-part of U.S. patent applicationSer. No. 10/818,555 filed Apr. 5, 2004 that is a continuation of U.S.patent application Ser. No. 10/464,633 filed Jun. 18, 2003, now U.S.Pat. No. 6,716,214, both of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery, and cooperating elongateconnecting members that are at least somewhat plastically deformable.Such screws have a receiver or head that can swivel about a shank of thebone screw, allowing the receiver to be positioned in any of a number ofangular configurations relative to the shank.

Many spinal surgery procedures require securing various implants to boneand especially to vertebrae along the spine. For example, elongatemembers, such as solid rigid rods are often utilized that extend alongthe spine to provide support to vertebrae that have been damaged orweakened due to injury or disease. Such elongate members must besupported by certain vertebrae and support other vertebrae.

The most common mechanism for providing vertebral support is to implantbone screws into certain bones which then in turn support the elongatemember or are supported by the elongate member. Bone screws of this typemay have a fixed head or receiver relative to a shank thereof. In thefixed bone screws, the head cannot be moved relative to the shank andthe rod or other elongate member must be favorably positioned in orderfor it to be placed within the head. This is sometimes very difficult orimpossible to do. Therefore, polyaxial bone screws are commonlypreferred.

Polyaxial bone screws allow rotation of the receiver about the shankuntil a desired rotational position of the receiver is achieved relativeto the shank. Thereafter, a rod or other elongate connecting member canbe inserted into the receiver and eventually the rod and the receiverare locked or fixed in a particular position relative to the shank.

A variety of polyaxial or swivel-head bone screw assemblies areavailable. One type of bone screw assembly includes an open head orreceiver that allows for placement of a rod or other elongate memberwithin the receiver. A closure top or plug is then used to capture therod in the receiver of the screw. Thus, the closure top or plug pressingagainst the rod not only locks the rod in place but also locks the bonescrew shank in a desired angular position with respect to the receiver.A draw back to such a system occurs when the rod or other elongateconnecting member is made from a material that exhibits creep orviscoelastic behavior. Creep is a term used to describe the tendency ofa material to move, flow or to deform permanently to relieve stresses.Material deformation occurs as a result of long term exposure to levelsof stress that are below the yield or ultimate strength of the material.Rods and other longitudinal connecting members made from polymers, suchas polyetheretherketone (PEEK), especially pure PEEK and rubbers, have agreater tendency to exhibit creep, than, for example metals or metalalloys, such as stainless steel, titanium and nickel titanium (commonlyreferred to by its trade name Nitinol). When a rod or other longitudinalconnecting member exhibits creep deformation over time, the closure topmay no longer tightly engage the connecting member. This in itself isnot necessarily problematic. However, such loosening also results inloosening of the frictional engagement between the receiver and the bonescrew shank that locks the angular orientation of the shank with respectto the receiver. Body movement and stresses may then result inundesirable pivoting of the shank with respect to the receiver causingmis-alignment, greater stress and further loosening of the variouspolyaxial bone screw components.

It is known to equip a bone screw assembly with an upper and/or a lowerpressure insert located within the receiver for engaging and closelyholding one or more surfaces of a rod or other longitudinal connectingmember. Nested closure tops are known in the art that include afastening portion having an outer thread for engaging an interiorthreaded surface of the receiver arms and also an inner thread forengaging a threaded set screw. The fastening portion of the closure topis disposed within the receiver arms but does not operationally abutagainst a rod or other longitudinal connecting member. Rather, thefastening portion abuts against one or more pressure inserts alsolocated in the receiver that in turn engage a polyaxial bone screwmechanism so that the shank may be set and locked at a desired angularposition with respect to the receiver prior to locking the rod or otherlongitudinal connecting member in place by direct or indirect pressurethereon by the independently rotatable inner set screw. However, one ofthe drawbacks to such a polyaxial implant is that to maintain arelatively non-bulky, low profile assembly, the numerous inserts andother component parts of such an assembly have thin walls that providethe desired low profile but otherwise lack sufficient strength towithstand the stresses placed thereon by the human body and othercomponent parts of the bone screw assembly. In order to remedy thisproblem, it is further known in the art to equip such an assembly withan outer nut (located outside of the receiver arms) to keep the arms ofthe receiver from splaying and aid in securely holding any inserts andother small component parts within the receiver of the bone screwassembly so that the parts do not loosen or disassemble within the body.However, such a nut adds undesirable bulk to the assembly and may leadto undesirable interference with vertebrae and other medical implants.

SUMMARY OF THE INVENTION

A polyaxial bone screw assembly of the present invention includes ashank having a generally elongate body with an upper end portion and alower threaded portion for fixation to a bone. The bone screw assemblyfurther includes a receiver having a top portion and a base. The topportion is open and has a channel. The base includes an inner seatingsurface partially defining a cavity and has a lower aperture or opening.The channel of the top portion communicates with the cavity, which inturn communicates with an opening to an exterior of the base. The shankupper portion is disposed in the receiver cavity and the shank extendsthrough the receiver base opening. A shank capture connection isprovided by the upper portion that includes a first helical guide andadvancement structure that mates with a second helical guide andadvancement structure on a retaining structure, the retaining structureconfigured for polyaxial motion with respect to the receiver. The shankhas an upper surface that exclusively engages a compression insert thatin turn engages a longitudinal connecting member being supported withinthe receiver. In certain embodiments, the compression insert includes aplanar seat and spaced planar sides for closely receiving a variety ofelongate connecting members including members having planar orcylindrical surfaces. A closure structure of the invention may be duallocking and include an outer fastener and an inner set screw. The outerfastener is sized and shaped for engaging the compression insertindependent of the longitudinal connecting member for securing theassembly in a wide range of angular orientations. The inner set screwexclusively engages the longitudinal connecting member. In anillustrated embodiment the outer fastener includes a pair of opposedflanges for interlocking engagement with a pair of opposed flange tracksof the receiver. In another embodiment, the outer fastener includes anouter helical flange for interlocking engagement with a discontinuoushelical guide and advancement structure located on the receiver.

Objects and Advantages of the Invention

Objects of the invention include one or more of the following: providinga polyaxial bone screw having a shank with an integral upper end portionthat threadably mates with a retaining structure configured forpolyaxial motion with respect to the receiver prior to locking;providing such a polyaxial bone screw that includes a pressure insertthat exerts pressure exclusively on an upper surface of the integral andstronger shank upper end portion, the upper surface being substantiallyspaced from the retaining structure; providing such an implant whereinall of the parts remain together and do not separate; providing alightweight, low profile polyaxial bone screw that assembles in such amanner that the components cooperate to create an overall structure thatprevents unintentional disassembly; providing a polyaxial bone screwthat provides independent locking for the bone screw shank and thelongitudinal connecting member; providing such an assembly that includesa longitudinal connecting member that may be of non-circular or circularcross-section; providing such an assembly that remains in a lockedposition even if the longitudinal connecting member undergoesdeformation such as creep; providing a polyaxial bone screw withfeatures that provide adequate frictional or gripping surfaces for boneimplantation tools and may be readily, securely fastened to each otherand to bone; and providing apparatus and methods that are easy to useand especially adapted for the intended use thereof and wherein theapparatus are comparatively inexpensive to make and suitable for use.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, partial and exploded perspective view of a bonescrew assembly according to the invention including a bone screw shank,a receiver, a lower compression insert and a closure structure having anouter fastener and an inner set screw and shown with a longitudinalconnecting member in the form of a rod.

FIG. 2 is an enlarged front elevational view of the receiver of FIG. 1.

FIG. 3 is an enlarged cross-sectional view taken along the line 3-3 ofFIG. 1.

FIG. 4 is an enlarged side elevational view of the receiver of FIG. 1.

FIG. 5 is an enlarged cross-sectional view taken along the line 5-5 ofFIG. 4.

FIG. 6 is an enlarged top plan view of the receiver of FIG. 1.

FIG. 7 is an enlarged side elevational view of the lower compressioninsert of FIG. 1.

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 7.

FIG. 9 is an enlarged top plan view of the lower compression insert ofFIG. 1.

FIG. 10 is an enlarged and partial perspective view of the shank,receiver and compression insert of FIG. 1, shown assembled.

FIG. 11 is a second enlarged and partial perspective view, similar toFIG. 10.

FIG. 12 is an enlarged side elevational view of the closure structure ofFIG. 1.

FIG. 13 is an enlarged top plan view of the closure structure of FIG. 1.

FIG. 14 is an enlarged top plan view of the set screw of the closurestructure of FIG. 1.

FIG. 15 is an enlarged and exploded front elevational view of theclosure structure of FIG. 1.

FIG. 16 is an enlarged perspective view of the closure structure of FIG.1 with portions removed to show the detail thereof.

FIG. 17 is an enlarged and partial front elevational view of theassembly of FIG. 1 shown in a stage of assembly and with portions brokenaway to show the detail thereof.

FIG. 18 is an enlarged and partial side elevational view of the assemblyof FIG. 1 shown fully assembled and with a break-off top removed.

FIG. 19 is a cross-sectional view taken along the line 19-19 of FIG. 18.

FIG. 20 is an enlarged and partial perspective view of the assembly ofFIG. 1 shown with a bar in lieu of the rod shown in FIG. 1 and withportions broken away to show the detail thereof.

FIG. 21 is an enlarged and partial front elevational view of theassembly shown in FIG. 20.

FIG. 22 is an enlarged, partial and exploded perspective view of asecond, alternative bone screw assembly according to the inventionincluding a bone screw shank, a receiver, a retaining structure, a firstlower compression insert, a second upper compression insert and aclosure member and shown with a longitudinal connecting member in theform of a rod.

FIG. 23 is an enlarged front elevational view of the closure member ofFIG. 22.

FIG. 24 is a cross-sectional view taken along the line 24-24 of FIG. 23.

FIG. 25 is an enlarged top plan view of the closure member of FIG. 23.

FIG. 26 is an enlarged perspective view of the upper compression insertof FIG. 22.

FIG. 27 is an enlarged front elevational view of the upper compressioninsert of FIG. 22.

FIG. 28 is an enlarged side elevational view of the upper compressioninsert of FIG. 22.

FIG. 29 is an enlarged and partial cross-sectional view of the closuremember, similar to FIG. 24 and further showing the upper compressioninsert in front elevation prior to attachment to the closure member.

FIG. 30 is an enlarged and partial cross-sectional view of the closuremember and front elevational view of the upper compression member,similar to FIG. 29, showing the upper compression member rotatablyattached to the closure member.

FIG. 31 is an enlarged front elevational view of the bone screw shank ofFIG. 22 with portions broken away to show the detail thereof.

FIG. 32 is an enlarged front elevational view of the receiver andretaining structure of FIG. 22 with portions broken away to show thedetail thereof and further showing the retaining structure in phantom inan early step of assembly of the bone screw assembly of FIG. 22.

FIG. 33 is an enlarged and partial front elevational view of thereceiver, the retaining structure and the bone screw shank of FIG. 22with portions broken away to show the detail thereof and shown in a stepof assembly subsequent to that shown in FIG. 32.

FIG. 34 is a reduced front elevational view of the receiver, the bonescrew shank and the retaining structure of FIG. 22 with portions brokenaway to show the detail thereof and shown with a tool driving the bonescrew shank into a vertebrae, also with portions broken away to show thedetail thereof.

FIG. 35 is an enlarged and partial front elevational view of thereceiver, bone screw shank, retaining structure and lower compressioninsert of FIG. 22 with portions broken away to show the detail thereofand shown with the rod illustrated in FIG. 22, also with portions brokenaway to show the detail thereof.

FIG. 36 is an enlarged and partial front elevational view of theassembly of FIG. 22 with portions broken away to show the detail thereofand further showing the upper compression insert and closure memberpartially inserted in the receiver.

FIG. 37 is an enlarged and partial front elevational view similar toFIG. 36 showing the upper compression insert and closure member fullyseated in the receiver prior to removal of the closure member break-offhead.

FIG. 38 is an enlarged and partial front elevational view of theassembly of FIG. 22 with portions broken away to show the detailthereof, and further showing the closure member break-off head removed.

FIG. 39 is an enlarged and partial front elevational view of analternative embodiment according to the invention, similar to theassembly of FIG. 22, but without the upper compression insert, shownassembled, with break-off top removed and with portions broken away toshow the detail thereof and further showing the assembly cooperatingwith a longitudinal connecting member in the form of a bar ofrectangular cross-section in lieu of the rod shown in FIG. 22.

FIG. 40 is an enlarged and partial front elevational view of anotherembodiment according to the invention, similar to the assembly of FIG.22, but with a different compression insert, shown assembled with thebreak-off top removed, with portions broken away to show the detailthereof and further showing the assembly cooperating with a longitudinalconnecting member in the form of a bar of rectangular cross-section.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of bone attachment assemblies of the applicationand cooperating connecting members in actual use.

With reference to FIGS. 1-21, the reference number 1 generallyrepresents an embodiment of a polyaxial bone screw apparatus or assemblyaccording to the present invention. The assembly 1 includes a shank 4that further includes a threaded body 6 integral with an upper portion8; a receiver 10; a lower compression insert 12; and a dual closurestructure, generally 14. The shank 4, receiver 10, and compressioninsert 12 are typically factory assembled prior to implantation of theshank body 6 into a vertebra (not shown). However, if desirable incertain situations, the shank may be implanted into a vertebra first andthereafter the receiver threadably connected thereto.

With further reference to FIG. 1, the closure structure 14 furtherincludes an outer fastener 18 and an inner set screw 20 for engaging alongitudinal connecting member such as a rod 21 having a cylindricalsurface 22 shown in FIGS. 1 and 17-19, for example, or a longitudinalconnecting member that does not have a circular cross-section, such asthe bar 24 having a square or rectangular cross-section and planarsurfaces 25 shown in FIGS. 20 and 21. The outer fastener 18 pressesagainst the compression insert 12 that in turn presses upon the shankupper portion 8 which biases the portion 8 into fixed frictional contactwith the receiver 10, so as to fix the rod 21 or the bar 24 relative tothe vertebra (not shown). The receiver 10 and the shank 4 cooperate insuch a manner that the receiver 10 and the shank 4 can be secured at anyof a plurality of angles, articulations or rotational alignmentsrelative to one another and within a selected range of angles both fromside to side and from front to rear, to enable flexible or articulatedengagement of the receiver 10 with respect to the shank 4 until both arelocked or fixed relative to each other near the end of an implantationprocedure. The rod 21 or the bar 24 may be advantageously manipulatedindependently of locking the shank 4 with respect to the receiver 10 andthen ultimately locked into place in the receiver 10 by rotation of theset screw 20 into direct engagement with the rod 21 or bar 24. Thus, ifthe rod 21 or the bar 24 is made from a material such as rubber or PEEK,that exhibits any viscoelastic flow or creep, any resultant loosening ofthe rod 21 or the bar 24 with respect to the set screw 20 would have noimpact on the security of the polyaxial locking of the shank 4 withrespect to the receiver 10 provided by the pressure placed on thepolyaxial mechanism by the outer fastener 18 through the insert 12.

With particular reference to FIGS. 1, 18 and 19, the shank 4 iselongate, with the shank body 6 having a helically wound boneimplantable thread 28 extending from near a neck 30 located adjacent tothe upper portion 8 to a tip 32 of the body 6 and extending radiallyoutwardly therefrom. During use, the body 6 utilizing the thread 28 forgripping and advancement is implanted into the vertebra (not shown)leading with the tip 32 and driven down into the vertebra with aninstallation or driving tool, so as to be implanted in the vertebra tonear the neck 30, and as is described more fully in the paragraphsbelow. The shank 4 has an elongate axis of rotation generally identifiedby the reference letter A.

The neck 30 extends axially upwardly from the shank body 6. The neck 30is of slightly reduced radius as compared to an adjacent top 33 of thethreaded body 6. Further extending axially upwardly from the neck 30 isthe shank upper portion 8 that provides a connective or captureapparatus disposed at a distance from the threaded body top 33 and thusat a distance from the vertebra when the body 6 is implanted in thevertebra.

The shank upper portion 8 is configured for a polyaxial connectionbetween the shank 4 and the receiver 10 and capturing the shank 4 upperportion 8 in the receiver 10. The neck 30 extends axially upwardly fromthe shank body 6 to a base 34 of the upper portion 8. The upper portion8 has an outer partially spherically shaped surface 40 extending fromthe base 34 to a planar top portion 42. Formed in the top portion 42 isan internal drive mechanism 44 illustrated as a hex drive. The internaldrive 44 is coaxial with the shank 4. The drive 44 is sized and shapedfor engagement with a driving tool (not shown) that is received by thedrive 44 so as to form a socket and mating projection combination forboth operably driving and rotating the shank body 6 into a vertebra.

The illustrated base 34 of the portion 8 has a smooth surface, but it isforeseen that the base 34 may have a high-friction or roughened surface,such as a scored or knurled surface. Formed on the spherical surface 40is a helical guide and advancement structure 48. The guide andadvancement structure 48 retains the substantially spherical outer shapeof the surface 40 at a crest thereof, but may be otherwise described asa substantially buttress thread form, sized and shaped to mate with acooperating guide and advancement structure 50 disposed on an innersurface 52 of the receiver 10 disposed adjacent to and defining anopening 54 of a lower end or bottom 56 of the receiver 10 (see FIGS. 2and 3). Preferably, the guide and advancement structure 48 is relativelythick and heavy to give strength to the thread and prevent the threadfrom being easily bent or deformed when axial pressure is applied to theshank 4 to maintain the upper portion 8 in the receiver 10. The guideand advancement structure 48 winds about the spherical surface 40 in agenerally helical pattern or configuration that is typical of threadsand can have various pitches, be clockwise or counterclockwise advanced,or vary in most of the ways that conventional buttress or square threadsvary. The guide and advancement structure 48 has a leading surface orflank 58 and a trailing surface or flank 59. As used herein, the termsleading and trailing refer to the direction of advancement of the upperportion 8 into the guide and advancement structure 50 of the receiver 10aligning the axis A of the shank 4 with an elongate axis of rotation Bof the receiver 10 and directing the upper portion 8 toward the receiver10, as shown by the straight arrow C illustrated in FIG. 1. Although thesubstantially buttress thread form 48 is described herein, it isforeseen that other thread types, such as square threads, V-threads,inverted thread types, other thread-like or non-thread-like guide andadvancement structures, such as flange form helically wound advancementstructures may be utilized according to the invention.

Advancement of the upper portion 8 into the receiver 10 is accomplishedby rotating the shank 4 in a clockwise or counterclockwise directionabout the axes A and B and into the receiver 10. A crest surface 60connecting the leading surface 58 and the trailing surface 59 is aloading surface after the upper portion 8 is fully disposed in thereceiver 10. Although discontinuous, the spherical surface 40 thatincludes the crest surface 60 has an outer radius that is approximatelyequal to a radius of an inner seating surface of the receiver 10,allowing for slidable mating contact between the surface 60 and theinner seating surface of the receiver 10.

An upper portion 62 of the spherical surface 40 located adjacent to thetop planar surface 42 is advantageously substantially spherical forsliding engagement and ultimate positive frictional mating engagementwith the compression insert 12, when the bone screw assembly 1 isassembled, as shown in FIG. 19 and in any alignment of the shank 4relative to the receiver 10. In certain embodiments, the surface 62 issmooth. While not required in accordance with the practice of theinvention, the surface 62 may be scored or knurled to further increasefrictional positive mating engagement between the surface 62 and thecompression insert 12.

The shank 4 shown in the drawings is cannulated, having a small centralbore 64 extending an entire length of the shank 4 along the axis A. Thebore 64 is defined by an inner cylindrical wall of the shank 4 and has acircular opening at the shank tip 32 and an upper opening communicatingwith the internal drive 44. The bore 64 provides a passage through theshank 4 interior for a length of wire (not shown) inserted into thevertebra (not shown) prior to the insertion of the shank body 6, thewire providing a guide for insertion of the shank body 6 into thevertebra (not shown).

To provide a biologically active interface with the bone, the threadedshank body 6 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

Referring to FIGS. 1-6 and 10-11, the receiver 10 has a generallysquared-off U-shaped appearance with a partially cylindrical innerprofile and a substantially faceted outer profile; however, the outerprofile could also be of another configuration, for example, curved orcylindrical. The receiver axis of rotation B, as shown in FIG. 1, isaligned with the axis of rotation A of the shank 4 during assembly ofthe receiver 10 with the shank 4 and the insert 12. After the receiver10 is pivotally attached to the shank 4, and the assembly 1 is implantedin a vertebra (not shown), the axis B is typically disposed at an anglewith respect to the axis A of the shank 4.

The receiver 10 includes a base 70 integral with a pair of opposedsubstantially similar or identical upstanding opposed arms 72 and 72′forming a squared-off U-shaped cradle and defining a channel 76 betweenthe arms 72 and 72′ with an upper opening 77 and a lower seat 78, thechannel 76 sized and shaped for operably receiving the rod 21 or the bar24. Each of the arms 72 and 72′ has an interior surface 80 and 80′,respectively, each having an inner cylindrical profile with opposedsloping interlocking flanged recesses or tracks 82 and 82′ configured tomate under rotation with a pair of opposed interlocking flange forms 84and 84′ on the fastener 18, as described more fully below. Each of thetracks 82 and 82′ run between and through pairs of parallel sidesurfaces 86 and 86′ of respective arms 72 and 72′. With particularreference to FIG. 19, each track 82 and 82′ is defined by a respectivelower substantially planar surface 88 and 88′ running about therespective cylindrical interior surface 80 and 80′; a respective outercylindrical surface 90 and 90′ running substantially parallel to therespective surfaces 80 and 80′, and a respective upper flanged portion92 and 92′ also running about the respective interior surfaces 80 and80′ and having a respective surface 94 and 94′ that extends downwardly(toward the base 70) and inwardly (toward the axis B) from therespective surface 90 and 90′. As best shown in FIG. 5, the tracks 82and 82′ are substantially identical in form and are located similarly onthe respective arms 72 and 72′ with the exception that such tracks slopein opposite directions, each having a higher end disposed near arespective planar stepped or lower top surface portion 96 and 96′ of therespective arms 72 and 72′ and a lower end disposed near a respectiveplanar upper top surface 98 and 98′ of the arms 72 and 72′. Therespective lower surfaces 96 and 96′ connected to respective uppersurface 98 and 98′ by respective planar walls or stops 100 and 100′. Thewalls or stops 100 and 100′ are each disposed parallel to the axis B.

Opposed tool engaging apertures 105 are formed on or through surfaces ofthe arms 72 and 72′ that may be used for holding the receiver 10 duringassembly with the shank 4 and the retainer structure 12 and also duringthe implantation of the shank body 6 into a vertebra (not shown). It isforeseen that tool receiving grooves or apertures may be configured in avariety of shapes and sizes and be disposed at other locations on thereceiver arms 72 and 72′. A pair of opposed spring tabs 106, each havingan upper body portion integral with a respective arm 72 or 72′, and alower insert engaging surface 110 extending downwardly and inwardly fromthe respective upper body portion. The tabs 106 are generally directedtowards the axis B and extend downwardly away from the guide tracks 82and 82′. The lower end surfaces 110 are thus positioned to engage thecompression insert 12 and hold such insert in a desired position as willbe described in greater detail below. The tabs 106 are typicallyinitially disposed parallel to the axis B and then a tool (not shown) isinserted into the aperture 105 from outside of the receiver 10 to engageand push the respective tab 106, thereby bending the tab 106 inwardly ina direction toward the axis B until the tab 106 is at a desired angularposition, such as is illustrated in FIG. 5. Such bending of the tabs 106may be performed either prior to or after assembly of the receiver 10with the shank 4 and the compression insert 12. In the illustratedembodiment, the tabs 106 are bent inwardly prior to installation withthe components 4 and 12. It is also foreseen that the tabs 106 may bemachined or otherwise pre-fabricated to be angled or directed toward theaxis B so as to engage the insert 12 as shown in the drawing figures.The illustrated tabs 106 are resilient, having a spring-like nature.Thus, when operatively cooperating with the insert 12, the tabs 106 biasagainst the insert 12, holding such insert in a desired position; andyet the tabs 106 are flexible enough to allow a user to make desiredadjustments of the position of the insert 12 within the receiver 10.

With further reference to FIGS. 1-5, communicating with and locatedbeneath the channel 76 of the receiver 10 is a chamber or cavity,generally 112, defined in part by an inner substantially cylindricalsurface 114 and also the lower internal surface 52 previously describedherein that includes the guide and advancement structure 50 and alsoincludes a substantially spherical seating surface portion 116. Thecylindrical surface 114 that defines a portion of the cavity 112 opensupwardly into the channel 76. The inner surface 116 that is locatedbelow the surface 114 is sized and shaped for mating with the shankupper portion 8 spherical surface 40 that includes the crest surfaces60.

As described above, the surface portion 116 is part of the inner surface52 that includes the opening 54. The opening 54 communicates with boththe cavity 112 and the receiver lower exterior or bottom 56 of the base70. The opening 54 is substantially coaxially aligned with respect tothe rotational axis B of the receiver 10. The opening 54 is also sizedand shaped to be smaller than an outer radial dimension of the shankupper portion 8 after the portion 8 has been threadably rotated throughthe opening 54, so as to form a restriction to prevent the portion 8from passing through the cavity 112 and out into the lower exterior 56of the receiver 10 during operation thereof.

With particular reference to FIGS. 1 and, 7-11 and 19, the compressioninsert 12 is sized and shaped to be received by and downloaded into thereceiver 10 through the opening 77. In operation, a portion of theinsert 12 is disposed between the rod 21 or the bar 24 and the upperportion 8 of the bone screw 4 as illustrated, for example, in FIG. 19.In operation, the closure structure 14 outer fastener 18 pressesdirectly upon the insert 12 that in turn presses upon the shank upperportion 8, pressing the upper portion 8 against the seating surfaceportion 116 of the receiver 10, resulting in frictional engagement andlocking of the angular position of the bone screw shank 4 with respectto the receiver 10 while allowing for further manipulation of the rod 21or bar 24 until such rod or bar is locked into place by engagement withthe inner set screw 20. The compression insert 12 has an operationalcentral axis D that is the same as the central axis B of the receiver10.

With particular reference to FIGS. 7-9, the compression insert 12 has acentral channel or through bore substantially defined by an innercylindrical surface 120 and an inner partially spherical surface 122,both having the central axis D. The compression insert 12 through boreis sized and shaped to receive a driving tool (not shown) therethroughthat engages the shank drive feature 44 when the shank body 6 is driveninto bone. The surface 122 is sized and shaped to cooperate with thespherical surface 62 of the shank upper portion 8 such that the surface122 slidingly and pivotally mates with the spherical surface 62. Thesurface 122 may include a roughening or surface finish to aid infrictional contact between the surface 122 and the surface 62, once adesired angle of articulation of the shank 4 with respect to thereceiver 10 is reached.

The compression insert 12 also includes a pair of arms 124 with asquared-off U-shaped surface or saddle 126 formed therebetween. Thesaddle 126 defines a channel that communicates with the bore defined bythe cylindrical surface 120 and the spherical surface 122. The saddle126 is substantially defined by a pair of planar opposed parallelsurfaces 128 and a planar bottom or seating surface 130, the surfaces128 and 130 being sized and shaped to closely receive the cylindricalrod 21 or the bar 24 planar surfaces 25. The saddle 126 extends from topsurfaces 132 to the bottom seating surface 130. A base having an outercylindrical surface 134 is disposed between the saddle 126 and anannular bottom surface 135. The cylindrical surface 134 also extendsabout the arms 124. Formed in the surface 124 and located centrally withrespect to each arm 124 outer cylindrical surface is a shallow groove136 having a substantially flat surface. In the illustrated embodiment asurface portion 137 disposed adjacent to each groove 136 and locatedbetween such groove 136 and the bottom surface 135 includes a pluralityof ridges or other roughened surface features. The grooves 136 are sizedand shaped to cooperate with the tabs 106 of the receiver 10 as will bedescribed in greater detail below. The roughened surface portions 137further cooperate with the tabs 106 to frictionally check or otherwiseprohibit relative movement between the tabs 106 and such surfaces 137during assembly and operation of the assembly 1. The grooves 136 may beof any shape, but are preferably elongate with the flat surface runningparallel to the axis D and having a width that receives the respectivetab 106. The illustrated bottom surface 135 is substantially planar andannular and disposed perpendicular to the axis D. Formed on the planarside surfaces 128 and also formed into the top surface 132 are a pair ofopposed recesses 138, each recess having a cylindrical surface 140running parallel to the axis D and a planar bottom surface 141 disposedperpendicular to the axis D. The recesses 138 are sized and shaped toprovide clearance for the inner set screw 20 of the closure structure 14as the set screw 20 is rotated down into engagement with the rod 21 orthe bar 24 as will be described in greater detail below.

The compression or pressure insert 12 ultimately seats on the shankupper portion 8 and is disposed substantially in the upper cylindricalportion 114 of the cavity 112, with the tabs 106 engaging the insert 12at the grooves 136, thereby holding the insert 12 in a desired alignmentwithin the receiver 10 as will be described in greater detail below. Inoperation, the insert 12 extends at least partially into the receiverchannel 76 such that the saddle 126 surface substantially contacts andengages the outer surface 22 of the rod 21 (or one of the planarsurfaces 25 of the bar 24) when such rod or bar is placed in thereceiver 10, keeping the rod or bar in spaced relation with the receiver10 lower seating surface 78.

FIGS. 1 and 12-16 illustrate the nested closure structure or closure top14 that includes the outer fastener 18 and the uploaded inner set screw20 that are coaxial along a central axis E that in operation is the sameas the axis B of the receiver 10. The fastener 18 further includes abase 146 integral or otherwise attached to a break-off head 148. Thebase 146 cooperates with the receiver 10 to capture the rod 21 or thebar 24 (or any other longitudinal connecting member) within the bonescrew receiver 10. The break-off installation head 148 is in the form ofa hex-shaped external drive feature having six planar surfaces 150 sizedand shaped for engagement with a socket tool (not shown) for installingthe fastener 14 to the bone screw receiver 10 and thereafter separatingthe break-off head 148 from the respective base 146 when installationtorque exceeds selected levels. A through slot 151 formed in a topsurface 152 of the break-off head 148 and disposed perpendicular to theaxis E may also be utilized to manipulate and/or rotate the closure 14.A through-bore 154 extends along the axis E completely through thefastener 18 from the top surface 152 of the break-off head 148 to abottom surface 156 of the base 146. As illustrated in FIG. 13, theportion of the bore 154 running through the break-off head 148 is sizedand shaped to receive and provide some clearance around a tool (notshown) engaging an inner drive 158 of the inner set screw 20.

The base 146 of the fastener 18 is substantially cylindrical, having anexternal surface 160. The flange forms 84 and 84′ project substantiallyradially and oppositely from the surface 160 near the bottom surface156. A pair of opposed substantially flat wing members 164 and 164′ alsoextend radially from the surface 160 and are located near a top surface166 of the base 146. The flanges 84 and 84′ are sized and shaped toslidingly mate with respective lower surfaces 88 and 88′, cylindricalsurfaces 90 and 90′ and flanged portions 92 and 92′ of the respectivetracks 82 and 82′ of the receiver 10. Inwardly facing surfaces 168 and168′ of the respective flanges 84 and 84′ slidingly cooperate and engagethe flanged portions 92 and 92′, respectively, to provide aninterlocking relationship between the fastener 18 and the receiver arms72 and 72′ and are thus splay resistant and do not exert radiallyoutward forces on the arms of the receiver 10, thereby avoidingtendencies toward splaying of the receiver arms when the fastener 18 istightly torqued into the receiver 10. The wing members 164 and 164′ areplate-like with upper and lower parallel substantially planar surfaces.The wing members 164 and 164′ are sized and shaped to slidingly matewith respective step surfaces 96 and 96′ of the receiver 10 and abutagainst respective surfaces 100 and 100′ when the flanges 84 and 84′ arerotated into a final fixed frictional engagement with respective tracks82 and 82′ as illustrated, for example, in FIGS. 19 and 20.

At the fastener base 146 the bore 154 is substantially defined by aguide and advancement structure shown in the drawing figures as aninternal V-shaped thread 176. The thread 176 is sized and shaped toreceive the threaded set screw 20 therein as will be discussed in moredetail below. Although a traditional V-shaped thread 176 is shown, it isforeseen that other types of helical guide and advancement structuresmay be used. Near a top of the base 146, an abutment shoulder 178,extends uniformly radially inwardly. The abutment shoulder 178 is spacedfrom the V-shaped thread 176 and sized and shaped to be a stop for theset screw 20, prohibiting the set screw 20 from advancing upwardly outof the base 146. It is foreseen that alternatively, the set screw may beequipped with an outwardly extending abutment feature near a basethereof, with complimentary alterations made in the fastener base 146,such that the set screw 20 would be prohibited from advancing upwardlyout of the top of the base 146 due to abutment of such outwardlyextending feature against a surface of the base 146.

An inner cylindrical wall 180 separates the abutment shoulder 178 fromthe thread 176. The cylindrical wall 180 has a diameter equal to orslightly greater than a root or major diameter of the internal thread176. The wall 180 partially defines a cylindrical space or passage foraxial adjustable placement of the screw 20 with respect to thelongitudinal connecting member 21 or 24.

The fastener break-off head 148 is integral or otherwise attached to thefastener base 146 at a neck or weakened region 182. The neck 182 isdimensioned in thickness to control the torque at which the break-offhead 148 separates from the fastener base 146. The preselectedseparation torque of the neck 182 is designed to provide secureengagement between the fastener base 146 and the lower compressioninsert 12 that in turn presses against the shank upper portion 8,clamping the shank 4 in a desired angular orientation with respect tothe receiver 10. The fastener 18 captures the longitudinal connectingmember 21 or 24 within the receiver 10 before the head 148 separates, byabutting against the lower compression insert 12 without making contactwith the rod 21 or the bar 24. For example, 120 inch pounds of force maybe a selected break-off torque to lock the bone screw shank in placewithout placing any pressure on the rod 21 or the bar 24. Separation ofthe break-off head 148 leaves only the more compact base 146 of thefastener 18 installed in the bone screw receiver 10, so that theinstalled fastener 18 has a low profile. As will be described in greaterdetail below, the set screw 20 may then be rotated and moved downwardlyinto secure engagement with the rod 21 or the bar 24. Thus, if the rod21 or bar 24 experiences viscoelastic flow and the engagement betweenthe screw 20 and the rod 21 or bar 24 is loosened, such loosening willnot loosen frictional engagement between the fastener base 146, theinsert 12, the shank upper portion 8 and the surface 116 of the receiver10.

The uploadable set screw 20 has a substantially annular and planar top186 and a substantially annular and planar bottom 187. The screw 20 issubstantially cylindrical in shape and coaxial with the fastener 18. Thescrew 20 includes an outer threaded cylindrical surface 188 extendingfrom the top 186 to the bottom surface 187. The v-shape thread of thesurface 188 is sized and shaped to be received by and mated with theinner thread 176 of the fastener base 146 in a nested, coaxialrelationship.

As illustrated, for example, in FIGS. 13, 14 and 19, the set screw 20includes a central aperture or drive 190 formed in the top 186 and sizedand shaped for a positive, non-slip engagement by a set screwinstallment and removal tool (not shown) that may be inserted throughthe bore 154 of the fastener 18 and then into the drive aperture 190.With particular reference to FIGS. 16, 17 and 19, the central set screwaperture 190 cooperates with the central internal bore 154 of thefastener 18 for accessing and uploading the set screw 20 into thefastener 18 prior to engagement with the bone screw receiver 10. Afterthe closure structure 14 is inserted and rotated into the tracks 82 and82′ of the bone screw receiver 10, and the break-off head 148 is brokenoff, the set screw 20 is rotated by a tool engaging the drive feature190 to place the set screw bottom 187 into frictional engagement withthe rod 21 or the bar 24. Such frictional engagement is thereforereadily controllable by a surgeon so that rod 21 or the bar 24 may bereadily manipulated until late in the surgery, if desired. Thus, at anydesired time, the set screw 20 may be rotated to drive the screw 20 intofixed frictional engagement with the rod 21 or the bar 24 withoutvarying the angular relationship between the receiver 10 and the bonescrew shank 4.

It is foreseen that the set screw 20 may further include a cannulationthrough bore extending along a central axis thereof for providing apassage through the closure 14 interior for a length of wire (not shown)inserted therein to provide a guide for insertion of the closure topinto the receiver arms 72 and 72′.

The elongate longitudinal connecting member that are illustrated in thisapplication include the cylindrical rod 21 and the bar 24 of square orother rectangular cross-section. A variety of shapes are possible,including but not limited to rods or bars of oval or other curved orpolygonal cross-section. Furthermore, the rod 21 or bar 24 may be acomponent of a dynamic stabilization connecting member, with thecylindrical or bar-shaped portions sized and shaped for being receivedby the insert saddle 126 also being integral or otherwise fixed to amore flexible, bendable or damping component that extends betweenadjacent pairs of bone screw assemblies 1. Such a rod or bar componentmay be made from a variety of materials including metal, metal alloys orother suitable materials, including, but not limited to plastic polymerssuch as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcomposites containing carbon fiber, as well as resorbable materials,such as polylactic acids.

With particular reference to FIGS. 1 and 17, prior to the polyaxial bonescrew assembly 1 being placed in use according to the invention, theshank upper portion is pre-loaded by insertion or bottom-loading intothe receiver 10 through the opening 54. The upper portion 8 is alignedwith the receiver 10, with the axes A and B aligned so that the buttressthread 48 of the upper portion 8 is inserted into and rotatingly matedwith the guide and advancement structure 50 on the receiver 10. Theshank 4 is rotated in a clockwise or counter-clockwise direction tofully mate the structures 48 and 50, and the rotation is continued untilthe thread 48 disengages from the thread 50 and the upper portion 8 isfully disposed in the receiver cavity 112. The shank upper portion 8 isthus in a slidable and rotatable engagement with the receiver 10, whilethe upper portion 8 is maintained in the receiver 10 with the shank body6 in pivotal or swivelable relation with the receiver 10. The shank body6 can be pivoted or rotated through a substantial angular rotationrelative to the receiver 10, both from side to side and from front torear so as to substantially provide a universal or ball joint. Thediscontinuous spherical surface 40 defined by the crest surface 60 is inslidable engagement with the receiver spherical seating surface 116.

The compression or pressure insert 12 is then inserted or top loadedinto the upper opening 77 of the channel 76 of the receiver 10 with thebottom surface 135 facing the top surface 42 of the shank upper portion8 and the arms 124 aligned with the arms 72 and 72′ of the receiver 10.As the insert 12 is moved downwardly toward the cavity 112, the tabs 106are received in respective grooves 136. The tabs 106 press against theinsert 12 at the grooves 136, allowing for some upward and downwardadjustment of the insert 12. However, rotation of the insert 12 aboutthe receiver axis B is prohibited by the tabs 106 abutting againstcylindrical surfaces of the arms 124 and upward movement of the insert12 out of the grip of the tabs 106 is further prohibited by the ridgesof the surface portion 137. Ridges defining the surface portion 137located at the lower curved portion of the grooves 136 also prohibit thetabs 106 from sliding along the outer cylindrical surface of the base134, thus resisting upward movement of the insert 12 out of the receiver10. As illustrated in FIG. 19, the insert 12 seats on the shank upperportion 8 with the surface 122 in sliding engagement with the surface62. The bone screw is typically factory assembled with the insert 12 asshown in FIGS. 10 and 11.

In use, the bone screw with assembled insert 12 (as shown in FIGS. 10and 11) is typically screwed into a bone, such as a vertebra (notshown), by rotation of the shank 4 using a driving tool (not shown) thatoperably drives and rotates the shank 4 by engagement thereof with theinternal drive 44. The vertebra (not shown) may be pre-drilled tominimize stressing the bone and have a guide wire (not shown) that isshaped for the cannula 64 and inserted to provide a guide for theplacement and angle of the shank 4 with respect to the vertebra. Afurther tap hole may be made using a tap with the guide wire as a guide.Then, the assembly 1 is threaded onto the guide wire utilizing thecannulation bore 64 by first threading the wire into the bottom opening32 and then out of the top at the internal drive 44. The shank 4 is thendriven into the vertebra, using the wire as a placement guide.

With reference to FIGS. 15 and 16, prior to implantation of the fastener14 into the receiver 10, the set screw 20 is inserted into the base 146of the outer fastener 18 at the bore 154 that opens to the bottomsurface 156. The screw 20 is rotated and drawn upwardly toward the topsurface 166 of the base 146, mating the threaded surface 188 with thefastener inner thread 176. Initially, the screw 20 is rotated until thescrew 20 is disposed entirely within the fastener 18 with the topsurface 186 of the screw 20 being closely adjacent to or in contact withthe abutment shoulder 178 as illustrated in FIG. 16.

With reference to FIG. 17, the rod 21 or other longitudinal connectingmember, such as the bar 24 shown in FIGS. 20 and 21, is eventuallypositioned in an open or percutaneous manner within the receiver channel76, and the closure structure 14 is then inserted into the receiver 10by placing the flange forms 84 and 84′ between the arms 72 and 72′followed by aligning the forms 84 and 84′ with the respective tracks 82and 82′ of the receiver 10. Such alignment also aligns the opposed wingmembers 164 and 164′ with the respective upper step surfaces 96 and 96′.With reference to FIG. 17, the closure structure is then rotated aboutthe axis B to mate the flange forms 84 and 84′ with the tracks 82 and82′. Alignment of the rod surface 22 or the bar surfaces 25 with respectto the receiver channel 76 and the saddle 126 of the insert 14 isinitially provided and then maintained by pressure placed at the insertgrooves 136 by the tabs 106. The closure fastener 14 is rotated, using atool engaged with the break-off head 148 hex drive 150 until a selectedpressure is reached at which point the head 148 separates from thefastener base 146. Also with reference to FIG. 17, at this time, the setscrew 20 is still entirely disposed within the base 146 and does notengage the rod 21 or the bar 24. However, the outer fastener 18 is inengagement with the insert 12 at the top surface 132 of the arms 124,placing the insert 12 surface 122 into frictional engagement with thesurface 62 of the shank upper portion 8 that in turn places the upperportion 8 into frictional engagement with the surface 116 of thereceiver 10, locking the shank 4 with respect to the receiver 10 in adesired angle with respect thereto. For example, about 80 to about 120inch pounds pressure may be required for removing the break-off head 148and fixing the bone screw shank 4 with respect to the receiver 10.

With reference to FIG. 19, the rod 21 (or bar 24) is eventually lockedinto place by utilizing a tool (not shown) inserted into the bore 154and into engagement with the set screw inner drive 158. The tool is usedto rotate the set screw 20 and drive the screw 20 downwardly until thesurface 187 is in frictional engagement with the rod 21 surface 22 (orthe bar 24 surface 25). With reference to FIGS. 17 and 19, as the screw20 advances downwardly toward the rod surface 22, the screw 20 remainsin spaced relation with the insert 12 with the recessed portions 138 ofthe insert 12 providing clearance for such downward advancement of thescrew 20. Thus, when the screw 20 is pressing firmly against the rod 21,the screw 20 does not make contact with any portion of the insert 12.Only the rod 21 (or bar 24) is pressed into frictional engagement withthe seating surface 130 of the insert 12. FIGS. 20 and 21 alsoillustrate that the set screw 20 may be rotated and driven downwardlyinto contact with the bar 24 (or the rod 21), if desired, prior to finaltorquing of the fastener 14 and removal of the break-off head 148.

As discussed above, if the frictional engagement between the set screw20 and the rod 21 (or the bar 24) eventually loosens due to creep orother viscoelastic flow of the rod 21 (or bar 24), such loosening willnot in turn loosen the lock between the receiver 10 and the bone screwshank 4. Therefore, the dual closure 14 advantageously allows for theuse with a variety of longitudinal members made from a wide range ofmaterials. As illustrated in FIGS. 20 and 21, the assembly 1advantageously cooperates with both cylindrical rods and with bars ofsquare or rectangular cross-section, such as the bar 24 of substantiallysquare cross-section. The bar 24 made from PEEK, for example, providesfor some dynamic, flexible support and yet due to the geometry thereofprovides greater support with respect to torsional forces, for example,than would a cylindrical PEEK rod. However, whether greater or lesserstability is required, the squared-off channel provided by the insert 12allows for the easy substitution of connecting members of round, square,rectangular or other cross-sectional shape.

It is noted that in certain embodiments according to the invention, asecond pressure insert may be located between the set screw 20 and therod 21 or bar 24. Furthermore, the rod 21 or the bar 24 may include acentral through bore or lumen (not shown) allowing for threading of suchrod or bar and implantation in a percutaneous or less invasiveprocedure.

If removal of the rod 21 or bar 24 from any of the bone screw assemblies1 is necessary, or if it is desired to release the rod 21 or bar 24 at aparticular location, such is accomplished by using the driving tool (notshown) that mates with the internal drive 158 on the set screw 20 torotate and first loosen the rod 21 or bar 24 from the receiver 10.Continued rotation of the set screw 20 causes the set screw 20 tocontact the abutment shoulder 178 and thereafter further rotation causesthe outer fastener 18 to disengage from the flange tracks 82 and 82′ ofthe receiver 10, thus removing the entire closure structure 14 from thecooperating receiver 10. Disassembly is then accomplished in reverseorder to the procedure described previously herein for assembly.

With reference to FIGS. 22-40, the reference numeral 201 generallydesignates an alternative polyaxial bone screw assembly according to theinvention for use with the rod 21 or the bar 24 previously describedherein with respect to the assembly 1 and also with a variety of rigidor dynamic stabilization longitudinal connecting member assemblies. Thebone screw assembly 201 is substantially similar to the bone screwassembly 401 disclosed in Applicant's US Patent Publication No.2007/0055244, published Mar. 8, 2007 (U.S. patent application Ser. No.11/522,503 filed Sep. 14, 2006) and incorporated by reference herein(hereafter the '244 publication) and illustrated in FIGS. 22-34 therein.There are a few exceptions, however, including a preferred polyaxialbone screw shank and retainer connection that allows for the lowerpressure insert to exclusively directly frictionally engage the bonescrew shank rather than pressing upon the retainer that is threadablyattached to the shank and configured for polyaxial motion with respectto the receiver; the addition of receiver spring tabs for holding thelower pressure insert in alignment; and squared-off channels formed bythe receiver and the lower pressure insert for closely receivingconnecting members of rectangular cross-section as well as cylindricalmembers, all of which will be described in greater detail in thefollowing paragraphs.

The bone screw assembly 201 of the present invention includes a shank204 that further includes a body 206 integral with an upwardlyextending, substantially cylindrical upper portion or capture structure208 operationally disposed primarily within a receiver 210. The shank204 is similar to the shank 414 disclosed in the '244 publication inthat the body 206 includes a helical thread 211 for attachment to avertebrae. The assembly 201 further includes a retainer in the form of aretaining and articulating structure 212 that is similar but notidentical to the retainer disclosed in the '244 publication. The shankupper portion 208 also includes a substantially spherically shaped upperor top surface 213 sized and shaped to slidingly mate with a lowerspherical surface of a lower pressure insert 214. Therefore, unlike thebone screw disclosed in the '244 publication, the pressure insert 214operationally presses directly against the shank upper portion 208 andnot the retainer 212. The shank 204, the receiver 210, the retaining andarticulating structure 212 and the first or lower compression insert 214are preferably assembled prior to implantation of the shank body 206into a vertebra. The shank body may include a cannulation bore 264similar in form and function to the bore 64 of the shank 4 of theassembly 1.

With particular reference to FIGS. 22 and 31-35, the shank upper portion208 further includes a substantially cylindrical portion 215 having ahelical thread 216 thereon, the portion 215 disposed adjacent to thespherical surface 213 and extending along an axial length thereof. Thethreaded cylindrical portion 215 flares or widens outwardly near an end217 thereof into a portion 218 of slightly greater diameter than aremainder of the cylindrical portion 215. The thread 216 or otherhelically wound guide and advancement structure is sized and shaped tomate with an inner portion 220 of the retainer 212 having a thread 221or other helically wound guide and advancement structure. The upperportion 208 further includes a top surface 222 having an internal drive223 formed therein for engaging with a driving tool (not shown) forrotating the shank 204 and driving the shank 204 into a vertebra (notshown). When the retainer 212 is mated with the shank upper portion 208,an outer substantially spherical surface 224 of the retainer 212 is insliding engagement with an inner substantially spherical seating surface228 of the receiver 210 as described previously herein with respect tothe upper portion 8 and the seating surface 116 of the assembly 1. Theretainer 212 further includes a sloped or frusto-conical top surface 225located between the inner threaded surface 220 and the outer sphericalsurface 224. In some embodiments of the invention the top surface 225may be planar. With particular reference to FIG. 35, the sloped surface225 advantageously provides for additional clearance between theretainer 212 and the lower pressure insert 214, ensuring that the insert214 engages only the bone screw shank at the surface 213 and not anyportion of the retainer 212.

With particular reference to FIGS. 23-30, the assembly 201 furtherincludes an upper insert 226 and a closure structure, generally 230,having an outer fastener 232 and an uploaded inner set screw 234. Theouter fastener 232 includes a base 236 integral or otherwise attached toa break-off head 238. The base 236 cooperates with the receiver 210 tocapture the rod 21 or the bar 24 within the bone screw receiver 210. Thebreak-off installation head 238 includes an internal drive or aperture240 sized and shaped for engagement with a tool (not shown) forinstalling the fastener 232 to the bone screw receiver 210 andthereafter separating the break-off head 238 from a respective base 236when installation torque exceeds selected levels.

The base 236 of the fastener portion 232 is substantially cylindrical,having an axis of rotation G and an external surface 250 having a guideand advancement structure 252 disposed thereon. The guide andadvancement structure 252 is matingly attachable to a guide andadvancement structure 253 of the bone screw receiver 210. Thecooperating guide and advancement structures 252 and 253 can be of avariety of types, including, but not limited to buttress threads,reverse angle threads, or square threads, and are preferably helicallywound flange forms that interlock and are splay resistant, and thus donot exert radially outward forces on the arms of the receiver 210,thereby avoiding tendencies toward splaying of the receiver arms whenthe fastener portion 232 is tightly torqued into the receiver 210.

The fastener portion 232 includes an internal, centrally located bore254. At the base 236, the bore 254 is substantially defined by a guideand advancement structure, shown in FIG. 24 as an internal V-shapedthread 256. The thread 256 is sized and shaped to receive the threadedset screw 234 therein as will be discussed in more detail below.Although a traditional V-shaped thread 256 is shown, it is foreseen thatother types of helical guide and advancement structures may be used.Near a top of the base 236, an abutment shoulder 260, extends uniformlyradially inwardly. The abutment shoulder 260 is spaced from the V-shapedthread 256 and sized and shaped to be a stop for the set screw 234,prohibiting the set screw 234 from advancing upwardly out of the base236. It is foreseen that alternatively, the set screw may be equippedwith an outwardly extending abutment feature near a base thereof, withcomplimentary alterations made in the fastener base 236, such that theset screw 234 would be prohibited from advancing upwardly out of the topof the base 236 due to abutment of such outwardly extending featureagainst a surface of the base 236.

An inner cylindrical wall 262 separates the abutment shoulder 260 fromthe thread 256. The cylindrical wall 262 has a diameter equal to orslightly greater than a root or major diameter of the internal thread256. The wall 262 partially defines a cylindrical space or passage 264for axial adjustable placement of the screw 234 with respect to thelongitudinal connecting member 21 or 24.

The fastener break-off head 238 is integral or otherwise attached to thefastener 232 at a neck or weakened region 266. The neck 266 isdimensioned in thickness to control the torque at which the break-offhead 238 separates from the fastener 232. The preselected separationtorque of the neck 266 is designed to provide secure engagement betweenthe fastener 232 and the lower compression structure or insert 214 thatin turn presses directly against the shank upper portion 208 that isthreadably mated to the retainer 212, pressing the retainer 212 againstthe receiver 210 and thus clamping the shank 204 in a desired angularorientation with respect to the receiver 210 and the rod 21 or the bar24. The fastener 232 thus captures the longitudinal connecting member 21or 24 within the receiver 210 before the head 238 separates, by abuttingagainst the lower compression member 214 without making contact with therod 21 or the bar 24. For example, 120 inch pounds of force may be aselected break-off torque to lock the bone screw shank in place withoutplacing any pressure on the rod 21 or the bar 24. The illustratedinternal driving feature 240 of the break-off head 238 enables positive,non-slip engagement of the head 238 by an installation and torquingtool. Separation of the break-off head 238 leaves only the more compactbase 236 of the fastener 232 installed in the bone screw receiver 210,so that the installed fastener 232 has a low profile. As will bedescribed in greater detail below, the set screw 234 may then be rotatedand moved downwardly into secure engagement with the rod 21 or the bar24.

The base 236 of the fastener 232 includes a planar bottom surface 268disposed substantially perpendicular to the axis G for abutting the topsurfaces 269 of arms of the compression insert 214. However, the bottomsurface may also be ramped or inclined as described in the '244publication (with cooperating ramped surface on the insert 214).

The uploadable set screw 234 has a substantially annular and planar top276 and a substantially annular and planar bottom 277. The screw 234 issubstantially cylindrical in shape and coaxial with the fastener 232.The screw 234 includes an outer cylindrical surface 278 disposed nearthe bottom 277 and a threaded surface 280 extending from the top 276 tothe cylindrical surface 278. The v-shaped thread 280 is sized and shapedto be received by and mated with the inner thread 256 of the fastenerbase 236 in a nested, coaxial relationship.

As illustrated, for example, in FIGS. 24 and 25, the set screw 234includes a central aperture 286 formed in the top 276 and defined byside walls 288 that define a driving feature similar to but of smallerdimensions than the driving feature 240 of the fastener 232. The drivingfeature further includes a seating surface or bottom 289, aiding in apositive, non-slip engagement by a set screw installment and removaltool (not shown) that may be inserted through the aperture formed by thedriving feature 240 of the fastener 232 and then into the aperture 286and into engagement with the walls 288 defining the set screw drivingfeature. A lower central aperture or bore 290 extends between thecentral aperture 286 and the bottom 277 of the set screw 234. The bore290 is sized and shaped to receive and hold an upper portion of theupper compression structure 226 as will be described more fully below.

With further reference to FIG. 24, the central set screw aperture 286cooperates with the central internal bore 254 of the fastener 232 foraccessing and uploading the set screw 234 into the fastener 232 prior toengagement with the bone screw receiver 220. After the closure structure230 is inserted and rotated in the bone screw receiver 210, and thebreak-off head 238 is broken off, the set screw 234 is rotated by a toolengaging the drive feature walls 288 to place the set screw bottom 277into frictional engagement with the rod 21 or bar 24.

There are circumstances under which it is desirable or necessary torelease the longitudinal connecting member 21 or 24 from the bone screwassembly 201. For example, it might be necessary for a surgeon tore-adjust components of a spinal fixation system, including thelongitudinal connecting member 21 or 24, during an implant procedure,following an injury to a person with such a system implanted. In suchcircumstances, the tool that engages and rotates the set screw 234 atthe driving feature 288 may be used to remove both the set screw 234 andattached fastener base 236 as a single unit, with the set screw 234contacting and contained within the base 236 by the abutment shoulder260. Thus, rotation of the set screw tool engaged with the set screw 234backs both the set screw 234 and the fastener base 236 out of the guideand advancement structure 253 in the receiver 210, thereby releasing thelongitudinal connecting member 21 or 24 for removal from the bone screwreceiver 210 or repositioning of the longitudinal connecting member 21or 24. It is foreseen that other removal structures such as side slotsor other screw receiving and engagement structures may be used to engagethe set screw 234 that is nested in the fastener base 236.

With particular reference to FIGS. 22 and 35-37, the lower compressioninsert 214 includes a substantially cylindrical body 310 integral with apair of upstanding arms 312. The body 310 and arms 312 form a generallysquared-off U-shaped, open, through-channel 314 with planar sidesurfaces 315 disposed perpendicular to a planar bottom seating surface316, the channel 314 and seating surface 316 sized and shaped to receiveeither the rod 21 or the planar surfaces 25 of the bar 24. In theillustrated embodiment, the channel surfaces 315 do not closely receivethe rod 21 and as will be described below, the rod 21 is heldsubstantially centrally in place by the upper compression insert 226.However, in other embodiments according to the invention, the lowerinsert may be sized and shaped to closely receive the rod 21 as well asthe bar 24 as shown in FIG. 34. The arms 312 of the inert 214 disposedon either side of the channel 314 each include a top flanged portion318, each portion 318 including the planar top surface 269 previouslydescribed herein, sized and shaped to engage the surface 268 of thefastener 232. The compression insert 214 further includes a bottomsurface 320 and a substantially cylindrical outer surface 322. An innercylindrical wall 324 defining a central through-bore extends along acentral axis of the compression structure 214 and extends between theseating surface 316 and a substantially spherical surface 326. Thesurface 326 extends between the inner cylindrical wall 324 and thebottom surface 320. The surface 326 is substantially similar to thespherical surface 122 of the compression insert 12 previously describedherein, the surface 326 being sized and shaped to frictionally engageand mate with the upper spherical surface 213 of the shank upper portion208.

The cylindrical surface 322 has an outer diameter slightly smaller thana diameter between crests of the guide and advancement structure 253 ofthe receiver 210 allowing for top loading of the compression insert 214.During top load installation, the top surface portions 318 disposed oneach of the upstanding arms 312 are inserted into the channel betweenthe receiver 210 upstanding arms and then the insert 214 is rotatedabout the axis F with the portion 318 sized and shaped to be receivedinto a run-out or recess located beneath the guide and advancementstructure 253. The receiver 210 fully receives the lower compressioninsert 214 and blocks the insert 214 from spreading or splaying in anydirection. It is noted that assembly of the shank 204 and the retainer212 within the receiver 210, followed by insertion of the lowercompression insert 214 into the receiver 210 are assembly stepstypically performed at the factory, advantageously providing a surgeonwith a polyaxial bone screw with the lower insert firmly snapped intoplace and thus ready for insertion into a vertebra. The through-channel314 is sized and shaped such that the upper compression structure orinsert 226 is receivable in the channel 314 between opposed uppersubstantially planar walls 315 that define the channel 314 from the base316 to the top surfaces 269. Adequate clearance is provided such thatthe upper compression insert 226 is in slightly spaced or in slidingrelationship with the walls 315, allowing for independent movement ofthe upper compression insert 226 with respect to the lower compressioninsert 214.

The lower insert 214 further includes opposed grooves 328 formed onouter surfaces of the arms 312. The grooves 328 are substantiallysimilar in form and function to the grooves 136 of the insert 12 of theassembly 1. The grooves 328 are sized and shaped to receive spring tabs329 of the receiver 210. The spring tabs 329 are similar in form andfunction to the tabs 106 previously described herein with respect to thereceiver 10 of the assembly 1 with the exception that the spring tabs329 extend from a lower portion of the receiver 210 in a directionupwardly toward the guide and advancement structure 253 as well asinwardly toward the axis F of the receiver 210.

With reference to FIGS. 26-30, the upper or second compression structureor insert 226 includes a body 330 having a pair of downwardly extendinglegs 332. The body 330 and the legs 332 form a generally U-shaped, open,through-channel having a substantially U-shaped seating surface 336having a radius substantially conforming to the outer radius of the rod21 and thus configured to operably snugly engage the rod 21 at theexternal surface 22 thereof opposite the seating surface 316 of thelower compression insert 214. FIG. 40 illustrates an alternativeembodiment wherein an upper insert 226′ includes a planar bottom surface338′ for engaging a planar top surface 25′ of a bar 24′. It is furthernoted that the polyaxial bone screw shank 204 and cooperating threadedretainer 212 capture connection provided in the assembly 201 may also beused without an upper pressure insert and in combination with the dualclosure structure 14 of the assembly 1, or alternatively, with aone-piece closure assembly.

Returning to the insert 226 of the assembly 201, the legs 332 eachinclude a bottom surface 338 that is substantially parallel to a planartop surface 340. The compression insert 226 includes a pair of opposedcurved outer surfaces 342 substantially perpendicular to the top surface340 and extending between the top surface 340 and the seating surface336. The curved surfaces 342 further extend along the legs 332 andterminate at the bottom surfaces 338. A pair of opposed substantiallyplanar outer surfaces 343 are disposed between the curved surfaces 342and are also disposed substantially perpendicular to the top surface340, each planar surface 343 extending between the top surface 340 and arespective bottom surface 338.

A pin 344 of substantially circular cross section is disposed centrallyon the top surface 340 and extends upwardly therefrom, being sized andshaped to fit within the centrally located lower bore 290 formed in theset screw 234. The pin 344 further includes a substantially cylindricalbase 346 and a U-shaped channel 348 formed by a pair of opposed, flangedarms 350 that extend from the base 346 upwardly and substantiallyparallel to one another. Each of the flanged arms includes a partiallyconical surface portion 351 and a flat bottom surface 352 that issubstantially parallel to the top planar surface 340 of the compressionstructure body 330. As illustrated in FIGS. 29 and 30, the pin 344 isreceivable in the bore 240 with surfaces forming the bore pressing anddeforming the flanged arms 350 toward one another as the uppercompression structure 226 is pressed against the set screw 234 that hasalready been up-loaded into a fastener portion 232. Once the conicalsurface portions 351 clear the bore 240 and enter the set screw aperture286, the flanged arms 350 return to the original upright andsubstantially parallel form with the surfaces 352 being in contact withand seated upon a portion of the bottom surface 289 as illustrated inFIG. 30. The flanged arms 350 thus keep the compression structure 226attached to the set screw 234 and yet rotatable with respect theretoabout an axis of rotation H of the cylindrical base 346 of the structurethat is coaxial with the axis G of the set screw 234 and fastener 232,providing a centered relationship between the closure structure 230 andthe compression structure 226 while allowing the compression structure226 to freely rotate into a position centered over and in grippingengagement with the longitudinal connecting member 21 when assembledthereon. Furthermore, if removal of the fastener and uploaded set screwis desired, the attached compression structure 226 is advantageouslyremoved along therewith.

With particular reference to FIGS. 24, 29, 30 and 36-38, in use, the setscrew 234 is assembled with the fastener 232 by inserting a set screwtool (not shown) through the bore 254 of the fastener 232 and into theaperture 286 of the set screw 234, with outer features of the toolengaging the inner walls 288 of the set screw 234. The set screw 234 isthen uploaded into the fastener 232 by rotation of the set screw 234with respect to the fastener 232 to mate the set screw thread 280 withthe fastener inner thread 256 until the set screw top surface 276 isspaced from the abutment shoulder 260, but substantially nested in thefastener 232, with possibly only the cylindrical surface 278 extendingfrom the fastener base 236. The upper compression structure 224 is thenattached to the set screw 234 as previously described with the pin 344being received by the bore 290 and inserted therethrough until the arms350 are disposed within the aperture 286, with the lower surfaces 352 ofthe flanged arms seated on the bottom 289 of the set screw aperture 286,capturing the flanged arms 350 within the aperture 286. The nestedassembly shown in FIG. 24 and attached to an upper compression structureas shown in FIGS. 29 and 30 is now pre-assembled and ready for use witha bone screw receiver 210 and cooperating rod 21.

With particular reference to FIGS. 22 and 32-35, the retainer 212 istypically first inserted or top-loaded, into the receiver squared-offU-shaped channel and then into the receiver cavity. Then, the retainer212 is rotated approximately 90 degrees so as to be coaxial with thereceiver 210 axis F and then seated in sliding engagement with the innerseating surface of the receiver 210 as shown in FIG. 32. With referenceto FIG. 33, the shank upper portion 208 is then inserted orbottom-loaded into the receiver 210. The retainer 212, now disposed inthe receiver 210 is coaxially aligned with the shank 204 and the upperportion 208 is generally rotated about the axis F mating the threadedsurface 215 with the threaded surface 220 of the retainer 212. Rotationcontinues until the retainer 212 engages the flared portion 218 and istightened thereon, fixing the retainer 212 to the shank upper portion208 as shown, for example, in FIG. 35. Preferably, the shank 204 and orthe retainer 212 are rotated to fully mate such structures at a factorysetting that includes tooling for holding and precisely rotating theshank 204 and/or the retainer 212 until locking frictional engagementtherebetween is accomplished. At this time both the shank 204 and theretainer 212 are in rotatable and swivelable engagement with thereceiver 210, while the shank upper portion 208 and the lower apertureor neck of the receiver 210 cooperate to maintain the shank body 206 inswivelable relation with the receiver 210. Only the retainer 212 is inslidable engagement with the receiver 210 spherical seating surface. Thespherical shank upper surface 213 is in spaced relation with thereceiver 210. The shank body 206 can be rotated and pivoted through asubstantial angular rotation relative to the receiver 210, both fromside to side and from front to rear so as to substantially provide auniversal or ball joint.

With reference to FIG. 35, the insert 214 may be top loaded into thereceiver 210 with the flanged portions 318 aligned in the receiverchannel, each flanged portion 318 being located between a pair ofopposed walls partially defining the receiver arms. The insert 214 isthen moved downwardly into the receiver and past the guide andadvancement structure 253. Once the flanged portions 318 are locatedbelow the guide and advancement structure 253 and adjacent the run-outrelief below the structure 253, the insert 214 is rotated about the axisF of the receiver 210 as illustrated by the arrow 380 in FIG. 22. Theflanged portions 318 fit within such relief. Once each flanged portion318 is located centrally with a respective arm of the receiver 210,rotation is ceased and the spring tabs 329 may be pressed into thegrooves 328 or the spring tabs 329 simply snap into the grooves 328 asin the illustrated embodiment of the receiver 210 wherein the tabs aredirected inwardly toward the axis F prior to assembly with the lowerpressure insert 214. The insert 214 is now locked into place inside thereceiver 210 with the guide and advancement structure 253 prohibitingupward movement of the insert out of the receiver 210 and the springtabs 329 that are biasing against the insert 214 at the grooves 328prohibiting rotational movement of the insert 214 with respect to thereceiver 210 about the receiver axis F. The insert 214 seats on theshank upper portion 208 with the partially spherical surface 326 insliding engagement with the cooperating partially spherical surface 213as best shown in FIG. 35 (and also shown in locked mated engagement inFIG. 38). It is noted that FIG. 35 illustrates the shank 204 andattached retainer 212 swiveled at an angle with respect to the receiver210 wherein the shank body 206 is extending forward from the plane ofthe drawing illustration as well as at an angle with respect to the twodimensions of the drawing figure. The run-out or relief under the guideand advancement structure 253 is sized and shaped to allow for someupward and downward movement of the insert 214 toward and away from theshank upper portion 208 such that the shank upper portion 208 is freelypivotable with respect to the receiver 210 until the closure structurefastener base 236 presses on the insert 214 that in turn presses uponthe upper portion 208 into locking frictional engagement with thereceiver 210. Similarly, the spring tabs 329 are sized, shaped andpositioned within the grooves 328 to allow for upward and downwardmovement of the insert 214 and pivoting of the shank 204 prior tolocking in place.

With reference to FIG. 34, in use, the bone screw shank 206 is typicallyscrewed into a bone, such as a vertebra 380 by rotation of the shank 204using a driving tool 382 that operably drives and rotates the shank 204by engagement thereof with the tool engagement structure 223. Withreference to FIGS. 35-37, the rod 21 is eventually placed in the bonescrew receiver 210 that has been previously attached to the bone screwshank 204 utilizing the retaining and articulating structure 212 andloaded with the lower compression insert 214. A driving tool (not shown)is used to rotate the closure structure by engagement with the drivefeature 240 of the break-off head 238, mating the guide and advancementstructures 252 and 253. During installation, the fastener surface 268frictionally engages the surface 269 of the lower compression insert214, that in turn presses the surface 326 exclusively against the shankupper portion 208 at the surface 213 at a location substantially spacedfrom the retainer 212 as shown in FIG. 38, biasing the retainer 212 atthe surface 224 into fixed frictional contact with the receiver 210 atthe seating surface 228, such that the receiver 210 and the shank 204can be independently secured at a desired angle with respect to thereceiver while the rod 21 remains movable within the receiver and yetsubstantially captured between the compression structures 212 and 226.Also with reference to FIG. 38, the closure structure is rotated until aselected pressure is reached at which time the head 238 breaks off,preferably about 80 to about 120 inch pounds that adequately fixes thebone screw shank 204 with respect to the receiver 210. When thebreak-off head is removed, the upper compression insert 226 ispreferably in contact with the rod 21, but placing little if anypressure thereon. Then, a set screw driving tool (not shown) is insertedinto the drive feature 288 and the set screw 234 is rotated downwardly,pressing against the insert 226 that in turn presses against the rod 21.

The polyaxial bone screw assembly 201 according to the inventionadvantageously allows for the removal and replacement of the rod 21 withanother longitudinal connecting member having a different overallcross-sectional width or outer diameter, utilizing the same receiver 210and the same lower compression insert 214. For example, as illustratedin FIG. 39, an assembly 201A is illustrated wherein the rod 21 isreplaced by the bar 24 and the upper insert 226 is not utilized.

With reference to FIG. 40, another assembly according the invention,generally 201B, includes a shank 204′, a receiver 210′, a set screw 234′and cooperating outer fastener 236′, and a lower insert 312′substantially similar to the respective shank 204, receiver 210, setscrew 234 and fastener 236, and insert 312 previously described hereinwith respect to the assembly 201. It is noted that the neck of the shank204′ is substantially cylindrical as compared to the curved neck of theshank 204. Shanks according to the invention may include a variety ofgeometries including, but not limited to straight cylinders, curvednecks, conical necks, and the like.

The assembly 201B further includes an upper insert 226′ that attaches tothe set screw 234′ in a manner similar to the previously describedcooperation between the set screw 234 and insert 226. However, theinsert 226′ includes a planar bottom surface 338′ for substantially fullfrictional contact with a planar surface 25′ of a bar 24′ of rectangularcross-section.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1-26. (canceled)
 27. A pivotable bone anchor assembly implantable in abone for mechanically coupling a longitudinal stabilization member tothe bone, the pivotable bone anchor assembly comprising: a receiverhaving a lower body with a bottom opening and a pair of upwardlyextending arms with opposed interior surfaces forming a receiver channelfor receiving a longitudinal stabilization member therebetween, theinterior surfaces having a discontinuous helically wound guide andadvancement structure formed thereon, and the lower body having a cavityin communication with the receiver channel and partially defined by apartially spherical-shaped inner surface adjacent the bottom opening,and an anchor member having a proximal end portion, a distal endportion, and a central opening extending entirely through the anchormember along a central longitudinal axis of the anchor member andopening onto a top end and a bottom end of the anchor member, thecentral opening being closed laterally along an entire length thereofand having a constant diameter at least along the distal end portion ofthe anchor member comprising an implant portion to be implanted into thebone, the proximal end portion including a partially spherical-shapedouter surface that is complimentary with the inner surface of thereceiver, wherein the proximal end portion of the anchor member isuploadable through the bottom opening of the receiver to establishpivotable motion between the anchor member and the receiver.
 28. Thepivotable bone anchor assembly of claim 27, wherein the proximal endportion of the anchor member further includes an attachment featureconfigured to receive a driving tool to drive the anchor member into thebone.
 29. The pivotable bone anchor assembly of claim 28, wherein theattachment feature further comprises an internal drive socket.